The invention relates to a method for data transmission via a radio interface and a radio communications system, which allow a macrodiversity reception.
In radio communications systems, information (for example voice, video information or other data) is transmitted via a radio interface using electromagnetic waves. The radio interface relates to a connection between a base station and subscriber stations. The subscriber stations may be mobile stations or stationary radio stations. The electromagnetic waves are in this case radiated at carrier frequencies which are in the frequency band intended for the respective system. Frequencies in the frequency band around about 2000 MHz are intended for future radio communications systems, for example UMTS (Universal Mobile Telecommunication System), or other 3rd generation systems.
Two modes are intended for 3rd generation systems. In a TDD (time division duplex) mode, the uplink direction (uplink being the direction from the mobile station to the base station) can be distinguished by different time slots within a frequency band. In an FDD (frequency division duplex) mode, there is one frequency band for the uplink direction, and one frequency bank for the downlink direction. Only the TDD mode will be described in the following text.
A radio communications system using the TDD mode is described, for example, in the German patent document DE 198 20 736, in which case the time slots in a frame are assigned or allocated to different base stations. These time slots are each used exclusively for transmission or reception by the base stations.
In the handover or transition region between two radio cells or sectors which are covered or serviced by different base stations, the transmission quality is normally subject to deterioration.
It is accordingly an object of the invention to provide a method and a system for transmitting data which overcome the above-mentioned disadvantages of the heretofore-known methods and systems of this general type and which improve the transmission quality of a data transmission via a radio interface.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for transmitting data via a radio interface between base stations and subscriber stations in a radio communications system. The method includes the steps of using a time-division multiplex process for organizing a radio interface within a frequency band such that a plurality of time slots constitute a frame; selectively using the time slots in one of an uplink direction and a downlink direction; allocating respective time slots of the plurality of time slots in the frame to respective base stations; transmitting, with the respective base stations, using exclusively the respective time slots allocated to the respective base stations for the downlink direction; receiving, with the respective base stations, in the respective time slots allocated to the respective base stations for the uplink direction as well as in further ones of the time slots not allocated to the respective base stations for the uplink direction; and combining received signals from at least two of the base stations for a macrodiversity reception.
In accordance with another mode of the invention, monitoring procedures are used in the base stations for determining time slots in the uplink direction not allocated to the respective base stations.
In accordance with yet another mode of the invention, a central unit reports to the respective base stations which of the time slots are not allocated to the respective base stations in the uplink direction.
In accordance with a further mode of the invention, the base stations report to each other the time slots in the uplink direction which are not allocated to the base stations.
In accordance with yet a further mode of the invention, the base stations for the different sector cells are installed at one location or, alternatively, are installed at different locations.
With the objects of the invention in view there is also provided, a radio communications system, including a first base station and a second base station, the first and second base stations having a radio interface for transmitting data in a downlink direction and for receiving data in an uplink direction; a radio resource controller connected to the first and second base stations for allocating radio resources and organizing the radio interface within a frequency band in accordance with a time-division multiplex scheme such that a plurality of time slots constitute a frame, each of the time slots being exclusively used in one of the uplink direction and the downlink direction; the first base station having a transmitter transmitting in a given one of the time slots allocated to the first base station for the downlink direction; the first base station having a first receiver for receiving in a further one of the time slots allocated to the first base station for the uplink direction; the second base station having a second receiver receiving in another one of the time slot allocated to the second base station for the uplink direction and receiving in additional ones of the time slots not allocated to the second base station for the uplink direction; and a combination device connected to the first and second base stations and combining received signals from the first and second base stations for a macrodiversity reception.
It is understood that the allocation of the time slots may change over time and that the transmitter may be allocated not just a single given time slot of a frame for transmitting but may be allocated a number of given time slots in a frame.
In accordance with another feature of the invention, the first receiver also receives in time slots not allocated to the first base station for the uplink direction.
In accordance with yet another feature of the invention, a subscriber station receives in the given one of the time slots allocated to the first base station for the downlink direction and transmits in the further one of the time slots allocated to the first base station for the uplink direction.
According to the invention, the time slots in a frame are allocated to different base stations in a radio communications system using the TDD mode. In the downlink direction, the base stations transmit exclusively in the time slots which are allocated to them, however, in the uplink direction, the base stations also receive in those time slots which are not allocated to them. It is thus possible to combine the received signals from at least two base stations with one another. The combination applies only to one transmission direction, the uplink direction.
The existing base stations, which are on standby during some time slots, can be used to provide a macrodiversity reception without any significant additional complexity. The transmission quality is improved by the plurality of propagation paths which are evaluated in the uplink direction.
The reception reliability is improved in boundary regions of radio cells, particularly in the case of sector cells, since the signals from at least two base stations can be received and the signals, which may be subject to interference, can be optimally combined. In the uplink direction, the method improves the power balance or transmission budget for a connection, such that the subscriber station can be operated even with a low transmission power and in poor transmission conditions, thus allowing longer call times and standby times.
The macrodiversity reception method improves the utilization of the hardware installed in a base station. This improved hardware utilization in the receiving device is in general, when considering an entire TDMA frame, independent of the number of time slots per frame allocated to a base station.
According to an advantageous embodiment of the invention, each base station uses a monitoring procedure and determines the time slots in the uplink direction which are not allocated to it. The monitoring procedure can distinguish between the time slots which are used in the uplink or downlink directions, on the basis of an evaluation of the received signals (Doppler shift, information content and information structure). According to this embodiment of the invention, no additional signaling complexity is required. Alternatively, it is possible for a central unit to report to the base stations not only the time slots in the uplink direction which are allocated to them but also the time slots in the uplink direction which are not allocated to them. This may be done within the allocation signaling or assignment signaling which, in the extreme case, would actually also have to include the allocation or assignment of all the time slots to one base station. A further embodiment of the invention provides that the base stations report to each other the time slots in the uplink direction which are allocated to them. For example, an evaluation of signaling channels of the radio interface of other base stations may in this case allow further information relating to the data transmission, such as the type of data transmission, to be additionally reported.
It is within the scope of the invention for the base stations for sector cells to be installed at one location or at different locations. The combination of the received signals is thus carried out either already within a base station complex at one location or in a central facility, which connects a plurality of base stations.
In particular, the invention can be used advantageously if the frequency band has a broad band width and signals which are transmitted at the same time within the frequency band differ on the basis of a connection-specific spread code. A large number of connections can be transmitted within one broad band frequency band, so that the diversity gain in this case can be used jointly for a number of connections, in the extreme case for all of them.
The combination of the received signals may be carried out within the physical layer through the use of an MRC combination (maximum ratio combination) or, in higher layers, by a selective combination.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and a system for data transmission with a macrodiversity reception, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.